A study of continuous rotation modes of detonation in an annular chamber with constant or increasing section

The detonation regime is an alternative to the conventional constant-pressure combustion mode typically used for propulsive systems because of its higher thermal efficiency and temperature and pressure of products, and shorter characteristic combustion time and length. The classic implementation is the rotating detonation engine, with the combustion chamber consisting of the annular space between a center-body and an outer cylindrical wall. This experimental study focuses on the effects of the chamber inner geometry, the total mass flow rate, and the detonation cell width on the conditions for detonation rotation. Cylindrical and conical center-bodies with several lengths and half-apex angles are considered to approach the hollow configuration of the RDE chamber. The cell width is varied by testing with mixtures of ethylene and enriched air, with several equivalence ratios and nitrogen dilutions. The combustion modes and the detonation velocities and pressures are characterized by analyzing pressure signals and high-speed camera visualizations. Three detonation regimes are identified, characterized by one or two fronts propagating in the same or opposite directions. Decreasing the center-body length and increasing the half-apex angle increases the measured detonation velocity and pressure. Velocities range between 53 and 89% of the Chapman–Jouguet value, and the pressure reaches about 11 bar. For the conditions tested, higher detonation velocity and pressure are obtained for the conical center-body configuration. Our interpretation is that center-bodies that are too long, or channels that are too narrow, hinder the exhaust of the burned gas. As a result, the proportion of products in the unburned gas mixture ahead of the detonation wave (consisting of fresh and burned gas) increases, resulting in a decrease in the magnitude of the detonation properties.